Baby Onesies to toddler underpants!

My 3.5 y/o son loves the idea of store bought character underpants, you know, Cars, Thomas, Diego hanes or Fruit of the Loom underwear.
unfortunately, the elastic they use is itchy and difficult for him to pull up/down comfortably.
therefore, for the past 1.5 years that he's been potty-trained, I've let him go, uh, commando.
he's getting old enough now, though, that it's time for him to start wearing proper skivvies.
I bought him some Cars underpants for xmas, in a size 6, thinking the larger size would make it easier.
NOPE!
so, I decided I needed to make him some again.
this plan coincided with a cleaning out of the garage.
we're not sure if our family is done growing or not, but neither my 3.5y/o boy, nor my 14m/o girl are wearing 12mo overtly-boy-print- onesies...
we were going to just donate them to charity, but then I decided that our budget would probably prefer it if I reused them, rather than donating and buying something else....
SO
here's the first one (basically a muslin, I'll make more of an effort to coordinate/match prints & colors from now on)

a kimono-style dinosaur onesie and a red/white striped onesie (with lots of stains) became a pair of size 6 (with size 8 waist/leg opening bands) toddler underpants!

I didn't bother making the boy-fly openings this time around, just trying to get the fit right.

I don't have a size 7 pattern, but I'll have to make one up, cause the 6 is too small/short, and the 8 is baggy.

but we're getting closer, he's worn these all day!